Protein kinases are a class of proteins (enzymes) that regulate a variety of cellular functions. This is accomplished by the phosphorylation of specific amino acids on protein substrates resulting in conformational alteration of the substrate protein. The conformational change modulates the activity of the substrate or its ability to interact with other binding partners. The enzyme activity of the protein kinase refers to the rate at which the kinase adds phosphate groups to a substrate. It can be measured, for example, by determining the amount of a substrate that is converted to a product as a function of time. Phosphorylation of a substrate occurs at the active-site of a protein kinase.
Tyrosine kinases are a subset of protein kinases that catalyze the transfer of the terminal phosphate of adenosine triphosphate to tyrosine residues on protein substrates. These kinases play an important part in the propagation of growth factor signal transduction that leads to cellular proliferation, differentiation and migration.
For example, fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) have been recognized as important mediators of tumor promoted angiogenesis. VEGF activates endothelial cells by signaling through two high affinity receptors, one of which is the kinase insert domain-containing receptor (KDR). See Hennequin L. F. et. al., J. Med. Chem., 2002, 45, 1300. FGF activates endothelial cells by signaling through the FGF receptor (FGFR). Solid tumors depend upon the formation of new blood vessels (angiogenesis) to grow. Accordingly, inhibitors of the receptors FGFR and KDR that interfere with the growth signal transduction, and thus slow down or prevent angiogenisis, are useful agents in the prevention and treatment of solid tumors. See Klohs W. E. et. al., Current Opinion in Biotechnology, 1999, 10, 544.
Other protein kinases include mitogen-activated protein kinases (MAP) which is a family of proline-directed serine/threonine kinases that activate their substrates by dual phosphorylation. One group of MAP kinases is the p38 kinase group which includes various isoforms (e.g., p38α, p39β, p38γ and p38δ). The p38 kinases are responsible for phosphorylating and activating transcription factors as well as other kinases, and are themselves activated by physical and chemical stress, pro-inflammatory cytokines and bacterial lipopolysaccharide.
More importantly, the products of the p38 phosphorylation have been shown to mediate the production of inflammatory cytokines, including TNF and IL-1, and cyclooxygenase-2. Each of these cytokines has been implicated in numerous disease states and conditions. For example, TNF-α is a cytokine produced primarily by activated monocytes and macrophages. Its excessive or unregulated production has been implicated as playing a causative role in the pathogenesis of rheumatoid arthritis. More recently, inhibition of TNF production has been shown to have broad application in the treatment of inflammation, inflammatory bowel disease, multiple sclerosis and asthma.
TNF has also been implicated in viral infections, such as HIV, influenza virus, and herpes virus including herpes simplex virus type-1 (HSV-1), herpes simplex virus type-2 (HSV-2), cytomegalovirus (CMV), varicella-zoster virus (VZV), Epstein-Barr virus, human herpes virus-6 (HHV-6), human herpesvirus-7 (HHV-7), human herpesvirus-8 (HHV-8), pseudorabies and rhinotracheitis, among others.
Similarly, IL-1 is produced by activated monocytes and macrophages, and plays a role in many pathophysiological responses including rheumatoid arthritis, fever and reduction of bone resorption.
Additionally, the involvement of p38 has been implicated in stroke, Alzheimer's disease, osteoarthritis, lung injury, septic shock, angiogenesis, dermatitis, psoriasis and atopic dermatitis. J. Exp. Opin. Ther. Patents, (2000) 10(1).
The inhibition of these cytokines by inhibition of the p38 kinase is of benefit in controlling, reducing and alleviating many of these disease states.
There are several examples of synthetic inhibitors for various protein kinases. Typically, kinase inhibitors block the phosphorylation of substrates by tightly interacting with the protein kinase ATP binding site (or “active site”). See WO 98/24432 and Hennequin L. F. et. al., J. Med. Chem., 2002, 45, 1300. Several of these compounds inhibit multiple targets. See also, PCT Publication Nos. WO 99/61444, WO 02/18380, and WO 01/64679; and U.S. Pat. No. 6,150,373;
However, there continues to be a need for compounds that are effective in inhibiting the catalytic activity of protein kinases, in particular FGF and KDR kinases for treating one or more types of solid tumors. It is particularly desirable to provide inhibitors that are selective for FGF and KDR. Selectivity is particularly desired due to a potential concomitant toxicity and other undesirable complications that may follow from inhibiting multiple targets. It is preferable that such inhibitors also possess advantageous bioavailability profiles.